[Sdcc-user] Differences between large and medium model for mcs51

[Mark S. <mark.swayne@q.com>]

What is the difference between the medium and large memory models for 
the mcs51?

The manual text is not clear on the exact differences:

3.17.1.1
...

When the medium or large model is used all variables declared without a 
storage class will be allocated into the
external ram, this includes all parameters and local variables (for 
non-reentrant functions). When the small model
is used variables without storage class are allocated in the internal ram.

Judicious usage of the processor specific storage classes and the 
’reentrant’ function type will yield much more
efficient code, than using the large model. Several optimizations are 
disabled when the program is compiled using
the large model, it is therefore recommended that the small model be 
used unless absolutely required.

Thanks,

--Mark Swayne